I assume you mean your Internet connection is failing intermittently. When I had that problem, I wrote a shell script that pinged my ISP's gateway address every minute and recorded the time of failures.

As jonPoz said, it gets set up on the authoritative ns. The only side note on that is that if you are running your own mail server behind pfSense and you want to use dkim, then you will more than likely need to add that to the pfSense DNS resolver, otherwise your mailserver will complain.

If you do want to add dkim, then just search for dkim on this site and you'll find I posted a thread about it.

Agree with johnpoz and marjohn56. If you need helping setting up DMARC (and SPF/DKIM), a group and I put together a technical guide at the link below if you are interested. It also has an associated testing guide which walks you through the process of discovering your authoritative nameservers.